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            <div><h3 class="title">
                <a name="asio.reference.synchronous_socket_operations"></a><a class="link"
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                                                                              title="Requirements on synchronous socket operations">Requirements
                on synchronous socket operations</a>
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    <p>
        In this section, <span class="emphasis"><em>synchronous socket operations</em></span> are those
        member functions specified as two overloads, with and without an argument
        of type <code class="computeroutput"><span class="identifier">error_code</span><span
            class="special">&amp;</span></code>:
    </p>
    <pre class="programlisting"><span class="bold"><strong><span
            class="emphasis"><em>R f</em></span></strong></span><span class="special">(</span><span
            class="emphasis"><em><span class="bold"><strong>A1</strong></span></em></span> <span
            class="identifier">a1</span><span class="special">,</span> <span class="emphasis"><em><span
            class="bold"><strong>A2</strong></span></em></span> <span class="identifier">a2</span><span class="special">,</span> <span
            class="special">...,</span> <span class="emphasis"><em><span
            class="bold"><strong>AN</strong></span></em></span> <span class="identifier">aN</span><span class="special">);</span>
<span class="bold"><strong><span class="emphasis"><em>R f</em></span></strong></span><span class="special">(</span><span
                class="emphasis"><em><span class="bold"><strong>A1</strong></span></em></span> <span class="identifier">a1</span><span
                class="special">,</span> <span class="emphasis"><em><span
                class="bold"><strong>A2</strong></span></em></span> <span class="identifier">a2</span><span
                class="special">,</span> <span class="special">...,</span> <span class="emphasis"><em><span
                class="bold"><strong>AN</strong></span></em></span> <span class="identifier">aN</span><span
                class="special">,</span> <span class="identifier">error_code</span><span
                class="special">&amp;</span> <span class="identifier">ec</span><span class="special">);</span>
</pre>
    <p>
        For an object <code class="computeroutput"><span class="identifier">s</span></code>, the conditions
        under which its synchronous socket operations may block the calling thread
        (C++Std [defns.block]) are determined as follows.
    </p>
    <p>
        If:
    </p>
    <p>
        — <code class="computeroutput"><span class="identifier">s</span><span class="special">.</span><span
            class="identifier">non_blocking</span><span class="special">()</span>
        <span class="special">==</span> <span class="keyword">true</span></code>,
    </p>
    <p>
        — the synchronous socket operation is specified in terms of a <span class="emphasis"><em>POSIX</em></span>
        function other than <code class="computeroutput"><a
            href="http://www.opengroup.org/onlinepubs/9699919799/functions/poll.html" target="_top"><code
            class="computeroutput"><span class="identifier">poll</span><span class="special">()</span></code></a></code>,
    </p>
    <p>
        — that <span class="emphasis"><em>POSIX</em></span> function lists <code class="computeroutput"><span
            class="identifier">EWOULDBLOCK</span></code>
        or <code class="computeroutput"><span class="identifier">EAGAIN</span></code> in its failure
        conditions, and
    </p>
    <p>
        — the effects of the operation cannot be established immediately
    </p>
    <p>
        then the synchronous socket operation shall not block the calling thread.
        [<span class="emphasis"><em>Note:</em></span> And the effects of the operation are not established.
        —<span class="emphasis"><em>end note</em></span>]
    </p>
    <p>
        Otherwise, the synchronous socket operation shall block the calling thread
        until the effects are established.
    </p>
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